The tweet came as world leaders met at the United Nations on Monday and approved a declaration aimed at providing a more coordinated and humane response to the global refugee crisis, of which Syrians make a substantial part.

Trump has aggressively advocated for a moratorium on accepting Syrian refugees and has spoken of erecting a wall on US-Mexico border to stop immigrants coming from Latin American countries.

He has criticised his opponent Hillary Clinton for encouraging the acceptance of about 65,000 Syrian refugees into the country, as she has expressed interest in expanding President Barack Obama's refugee programme.

Younger Trump's remark prompted a Twitter response from Mars Global, the parent company of Wrigley, which produces Skittles.

"Skittles are candy. Refugees are people. We don't feel it's an appropriate analogy," said the statement. "We will respectfully refrain from further commentary as anything we say could be misinterpreted as marketing."